Phosphorus-containing compounds, such as phosphite compounds, are desirable for use as stabilizers for plastics and particularly for rubbers, especially for their metal chelating properties. Hindered phenols are also considered to be desirable as antioxidants, as evidenced by the wide use and acceptance of butylated hydroxy toluene. However, any efforts to form compounds which are combinations of hindered phenols and phosphite esters, to take advantage of the properties of both classes of compounds, have failed because the hindered phenol hydrogen is unreactive. This unreactivity of the hindered phenol is evidenced by the fact that reaction with sodium in liquid ammonia is necessary to replace the phenolic hydroxyl. U.S. Pat. No. 3,244,661 discloses triaryl phosphites, but these are not phosphite ester of hindered phenols. Thus, this relatively recent example of the state of the art supports the generally recognized theory that phosphite esters of hindered phenols are not obtainable.
It has now been found that phosphite esters of hindered phenols, particularly bis phenols, can be prepared and are particularly valuable as stabilizers for plastics and rubbers.